[Imp]

Why not set yourself up a test to get to grips with it. AA units versus mixed ground units using the opfire filter. Once you have that working correctly add planes or helicopters & use the Y key to adjust the range against them.

Opfire sets behaviour against ground units.
Y key sets range versus ALL units.
Y key overrules opfire so if you set the range shorter than its set in the opfire it will use the Y setting.

So for AA to engage mainly air its simple set the opfire ranges low. Now set your AA range if desired using the Y key as I assume it will be larger.